Positron emission tomography (PET) is an in vivo imaging method that uses positron emitting radiotracers to track the biochemical, molecular, and/or pathophysiological processes in humans and animals. In PET systems, positron-emitting isotopes serve as beacons for identifying the exact location of diseases and pathological processes under study without surgical exploration of the human body. With these non-invasive imaging methods, the diagnosis of diseases may be more comfortable for patients, as opposed to the more traditional and invasive approaches, such as exploratory surgeries.
During PET imaging, PET gamma ray detectors (i.e., cameras or scanners) detect pairs of gamma rays that are emitted by the radiotracers. The PET detectors are periodically calibrated to assure function and accuracy of the equipment. Calibration may involve imaging of a calibration device (sometimes referred to as a calibration source) that includes a source of radioactive material that emits a known amount of radiation. The PET camera or scanner images the device and the results are compared to the amount of radiation the device was expected to emit based on the amount of radioactive material in the calibration device and/or based on measured activity.
One group of calibration devices is based on decay of germanium-68 (“Ge-68”). Ge-68 has a half-life of about 271 days, decays by electron capture to Ga-68, and lacks any significant photon emissions. These properties make germanium-68 an ideal material for calibrating PET scanners and cameras. A plastic matrix is sometimes used to hold various calibration sources, however this approach sometimes suffers from leaching during use and is sometimes structurally weak. Resins used as a matrix may deteriorate and form gas inside the material.
There is a need for improved germanium-68 source materials for calibrating radiation scanners and cameras and for calibration devices that incorporate such materials.
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